Six Ways to Cool the Earth and Why They’ll Never Happen

Make the clouds fluffier. Build a giant umbrella over the sun.
Photographer: Matt Knighton/Volvo Ocean Race via Getty Images

Big idea: Spray salt water into clouds at sea to make them fuller and whiter so they reflect sunshine away from earth.

Why it’ll never happen: Requires a massive, worldwide cloud-seeding operation to cool things just a little.